Eighty-five percent of American men say the last person they had sex with had an orgasm. And yet, only 64 percent of American women say they had an orgasm the last time they had sex. What's going on, guys?

The "orgasm gap"—which is too big to be explained away by men whose most recent sexual encounter was with another man—is one of the findings of a huge new national sex survey, the largest since 1994, undertaken by Indiana University's Center for Sexual Health Promotion and published in a special issue of the Journal of Sexual Medicine available here.

What are men doing wrong? Besides being really gullible? According to the survey, "women are more likely to orgasm when they engage in a variety of sex acts and when oral sex or vaginal intercourse is included," so maybe, you know, uh, switch it up a little more. You know, in bed. If you catch my drift. Sexually. (Women, if you're looking for a tip, here it is: "Men are more likely to orgasm when sex includes vaginal intercourse.")

What else did they learn about Americans in the sack?

Americans are freaks. Some 41 different "combinations of sexual acts" were counted as answers to questions about responder's most recent sexual activity. Bonus points to anyone who can list them all in the comments.

Plenty of people "experiment." About 7 percent of adult women and 8 percent of adult men identify as gay or bisexual, but higher proportions have engaged in what scientists call "gay stuff" during their lives. The most "experiment-y"? Almost 17 percent of women aged 20-24 have received oral sex from another women during their lives, many of them outside the context of "Girls Gone Wild" videos.

Everyone loses their virginity in high school. Ten percent of boys and 12.4 percent of girls aged 14-15 said they'd had vaginal intercourse in the past year. By the time they were 18-19, 62.5 percent of boys and 64 percent of girls had engaged in vaginal intercourse, usually after a series of comic misadventures easily compressed into a 90-minute runtime.

And here's a table of sexual behavior in the last year. Click to enlarge: